WO2009129458A2 - Procédé de production de silicium - Google Patents

Procédé de production de silicium Download PDF

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Publication number
WO2009129458A2
WO2009129458A2 PCT/US2009/040949 US2009040949W WO2009129458A2 WO 2009129458 A2 WO2009129458 A2 WO 2009129458A2 US 2009040949 W US2009040949 W US 2009040949W WO 2009129458 A2 WO2009129458 A2 WO 2009129458A2
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Prior art keywords
silicon
sodium
source
fluoride
fsa
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PCT/US2009/040949
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English (en)
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WO2009129458A3 (fr
Inventor
Leonard Nanis
Shi Yuan
Matthew Forkin
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CIRCULON HUNGARY Ltd
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CIRCULON HUNGARY Ltd
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Publication of WO2009129458A2 publication Critical patent/WO2009129458A2/fr
Publication of WO2009129458A3 publication Critical patent/WO2009129458A3/fr
Anticipated expiration legal-status Critical
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    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B33/00—Silicon; Compounds thereof
    • C01B33/02—Silicon
    • C01B33/021—Preparation
    • C01B33/027—Preparation by decomposition or reduction of gaseous or vaporised silicon compounds other than silica or silica-containing material
    • C01B33/03—Preparation by decomposition or reduction of gaseous or vaporised silicon compounds other than silica or silica-containing material by decomposition of silicon halides or halosilanes or reduction thereof with hydrogen as the only reducing agent
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B33/00—Silicon; Compounds thereof
    • C01B33/08—Compounds containing halogen
    • C01B33/10—Compounds containing silicon, fluorine, and other elements
    • C01B33/103—Fluosilicic acid; Salts thereof
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B33/00—Silicon; Compounds thereof
    • C01B33/08—Compounds containing halogen
    • C01B33/107—Halogenated silanes
    • C01B33/10705—Tetrafluoride
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B33/00—Silicon; Compounds thereof
    • C01B33/20—Silicates
    • C01B33/24—Alkaline-earth metal silicates

Definitions

  • the present invention relates to a method to make pure fluorosilicic acid
  • FSA fluorosilicate
  • the pure SFS When heated, the pure SFS provides pure gaseous silicon tetrafluoride for reaction with sodium metal, yielding pure silicon as a product
  • the first object is achieved by providing a process for synthesizing fluorosilicic acid comprising the steps of providing a source of silicon consisting essentially of silica, providing a source of fluoride ions, providing a source of sodium ions, reacting the source of silicon with the fluoride ions to form fluorosilicic acid (FSA), reacting the sodium ion with FSA to precipitate sodium fiuorosilicate (SFS) and generate hydrofluoric acid, and separating the precipitated SFS from the reaction mixture of the previous step.
  • FSA fluorosilicic acid
  • FSA fluorosilicic acid
  • SFS sodium fiuorosilicate
  • a second aspect of the invention is characterized by a process for synthesizing silicon comprising the steps of providing a source of silicon consisting essentially of silica, providing a source of fluoride ions, providing a source of sodium ions, reacting the source of silicon with the fluoride ions to form fluorosilicic acid (FSA), reacting the sodium ions with FSA to precipitate sodium fiuorosilicate (SFS) and generate hydrofluoric acid, separating the precipitated SFS from the reaction mixture of the previous step, decomposing the SFS to generate silicon tetrafluoride gas, reacting the silicon tetrafluoride gas with sodium to produce metallic silicon and sodium fluoride.
  • FSA fluorosilicic acid
  • FSS sodium fiuorosilicate
  • aspects of the invention include re-cycling the sodium fluoride and/or hydrofluoric acid by products for reaction with the source of silicon that consists essentially of phosphorus and boron free silica.
  • One aspect of the present invention is a method to make pure fluorosilicic acid (FSA) as a precursor feedstock for the production of pure silicon fluorosilicate (SFS).
  • FSA fluorosilicic acid
  • SFS pure silicon fluorosilicate
  • the pure SFS provides pure gaseous silicon tetrafluoride for reaction with sodium metal, yielding pure silicon as a product.
  • the rapidly growing silicon solar cell industry competes with the semiconductor industry for silicon, which is thus in short supply.
  • the purity requirements for solar grade silicon are different from those of semiconductor grade silicon. Whereas very low levels of phosphorus (P) and boron (B) are desirable in semiconductor silicon, less pure silicon with much greater initial P and B content can be tolerated for solar grades.
  • P phosphorus
  • B boron
  • a known reaction sequence for producing low cost silicon starting with low cost FSA by-product from the phosphate fertilizer industry also carries over P and B to precipitated SFS and to end product silicon which thus limits use to solar cells only. What is needed is an alternative low cost source of clean FSA with low levels of P and B to replace phosphate fertilizer by-product FSA.
  • the goal of this invention is to increase the supply of high purity silicon which can serve the dual purpose of meeting the purity requirements of both the semiconductor and solar industries.
  • the preferred feedstock is identified as commercial grade 23 weight percent FSA, a by-product of the phosphate fertilizer industry.
  • FSA sodium fiuorosilicate
  • NaF solid sodium fluoride
  • a purpose of this invention is to obtain low cost, clean FSA (and SFS) which will avoid the P and B impurities associated with FSA by-product of the phosphate fertilizer industry.
  • the "wet-process" for phosphate fertilizer manufacture contributes phosphorous and boron as impurities to FSA and ultimately to SFS and to sodium reduced silicon.
  • the wet process is so-named because sulfuric acid reacts with phosphate ore to yield the desired phosphoric acid and difficult to dispose by-products FSA and calcium sulfate (gypsum).
  • the present invention recognizes that the chemistry of the side reactions that yield byproduct liquid FSA and solid gypsum may be isolated and harnessed so as to produce clean FSA and thus clean SFS and silicon.
  • the present invention uses naturally occurring pure silicon dioxide (silica) as a low cost source of FSA.
  • Pure silica is abundant and is less expensive per weight of contained silicon than commercially available FSA.
  • the key ingredients to produce clean FSA are the combination of silica, an acid, preferably sulfuric acid, and a source of fluoride ion, preferably calcium fluoride (fluorite) or more preferably sodium fluoride.
  • fluoride ion preferably calcium fluoride (fluorite) or more preferably sodium fluoride.
  • By-product sodium fluoride from the sodium metal reduction of silicon tetrafluoride (Equation 3) can provide a recycled source of sodium fluoride. Conversion steps of FSA to SFS to silicon will be able to avoid phosphorus and boron and other impurities associated with phosphate by-product FSA.
  • the purity of silicon produced starting with the FSA of this invention may qualify it for dual purpose use ⁇ both for semiconductor devices and solar cells. Background
  • silicon obtained from waste by-product FSA contains a high proportion of the elements boron, B, and phosphorus, P.
  • B and P are active ingredients diffused purposely into silicon wafers (doping) in the fabrication of solar cells.
  • P is frequently diffused into silicon to define the n-p junction, typically to a depth of about 4000 Angstrom.
  • the requirements for low background B and P concentration levels in semiconductor structures are more stringent than for solar applications.
  • a low initial level of impurity B and P is desirable as a convenient reference starting point for controlled process doping additions.
  • a goal of the present invention is to develop a simple means to get the P and B out of the silicon in order to have dual purpose material for both photovoltaics and semiconductor wafer fabrication. Methods have been suggested in the literature for purifying commercial FSA such as the use of membranes. However, the present invention is a simple and straightforward method to reduce B and P content by completely avoiding these elements at the very front end of processing.
  • the present invention provides a novel path to get clean FSA by modifying and controlling the secondary chemical reactions that generate FSA as a phosphate fertilizer by-product.
  • the starting material for the present invention is clean, low cost silica as the primary source of silicon.
  • Better control of the FSA producing reactions is obtained by starting with a defined amount of silica and fluoride ion rather than depend on the highly variable content of siliceous material in phosphate rock ore.
  • the present invention permits improved control of the reaction rate by pre-selection of the particle size of pure silica and also of solid fluoride compound added to provide the fluoride ion required for the formation of FSA by acid digestion of silica according to Eqn 2B.
  • Fluoride ion for silica digestion may also be obtained from the solution of NaF resulting from aqueous leaching used to separate the mixture of solid NaF and Si produced by the Na-SiF 4 reaction Eqn 4.
  • silicon is not part of the apatite crystal structure.
  • the silicon is in a different rock, principally silicates and silicon dioxide (quartz) which just happens to be naturally mixed in with the phosphate -bearing rock.
  • the ore may also contain calcium carbonate, CaCO 3 , the mineral "calcite.”
  • Eqn 2A As apatite mineral is attacked by sulfuric acid (Eqn 2A), the fluorine component of the apatite of the mineral is solubilized into the aqueous acid solution as fluoride ion.
  • Eqn 2A is a plausible overall chemical sequence useful for the purpose of material balance calculations although it is understood that the overall chemistry may be composed of several intermediate reaction steps. It is postulated that the fluoride ion released from the apatite and some of the hydrogen ion from the sulfuric acid temporarily associate in solution, providing a chemical activity equivalent to hydrofluoric acid (HF). The acidified fluoride ion immediately proceeds to attack any silica present to form the by-product FSA according to the reaction in Eqn 2B. The reaction between sulfuric acid and apatite forms phosphoric acid (the desired fertilizer product) and also by-product calcium sulfate CaS ⁇ 4 (gypsum).
  • sulfuric acid is the source of hydrogen ions conventionally used in phosphate processing
  • the hydrogen ion can come from other acids as well.
  • the present invention is to purposely make FSA as a primary reaction product without getting involved with phosphate ore chemistry.
  • Carefully selected silica will serve as the source of silicon and a selected fluoride compound will provide fluorine for H 2 SiF 6 (FSA). Purity will be maintained in the subsequent reaction to form a precipitate of SFS by the use of selected pure sources of sodium ion.
  • Recycled by-product sodium fluoride (NaF) from the reaction of Eqn 4 that is the process of using the SFS to generate (SiCW) SiF 4 for reaction with liquid sodium to produce Silicon metal and sodium fluoride (NaF)
  • Eqn 3 Recycled by-product sodium fluoride
  • Chiotti also reported aluminum as a major impurity in commercial grade SFS with 1250 ppmwt Al in the first source sample and 930 ppmwt in the second source sample. It is noted that aluminum is also a frequently used dopant for silicon in semiconductor technology.
  • An advantage of using the thermal decomposition of SFS (Eqn 3) to provide silicon tetrafluoride as the silicon-containing reactant for reaction with sodium (Eqn 4) is that non-volatile impurity compounds remain in the NaF residue and do not transfer over into the reactor.
  • some B and P is known to transfer to the silicon produced by reaction between sodium and silicon tetrafluoride (Eqn 4) following generation of SiF 4 from thermal decomposition of SFS (Eqn 3).
  • B and P may be tolerable for photovoltaic silicon, it is instructive to compare them in Table 1 with the B and P levels customarily encountered in "pure" silicon used for semiconductor device processing.
  • Table 1 also includes concentrations of B and P in SFS precipitated from commercial grade FSA, as reported by SRI, supra.
  • Highly refined float zone silicon can have as little as 10 to the 1 lth (10 11 ) atoms per cc of boron.
  • 10 to the 14th (10 ) atoms per cubic centimeter is the equivalent of 0.002 parts per million by weight, clearly well below the P levels in silicon produced by the reaction in Eqn 4, as reported by SRI.
  • the present invention will minimize P and B impurity levels in the final silicon product by making clean FSA and SFS.
  • the straightforward approach of generating freshly made FSA starts with pure silica as feedstock. Pure silica with 99.7 weight percent or better SiO 2 is commercially available in several forms and is in abundance throughout the world.
  • Silica is reacted with an acid, such as hydrofluoric acid or sulfuric acid plus NaF to form a source of fluoride ions that react with the silica to form several by-products that can be used or purified to form Silicon Tetrafiuoride (STF).
  • an acid such as hydrofluoric acid or sulfuric acid plus NaF
  • STF Silicon Tetrafiuoride
  • the acid is sulfuric acid (H 2 SO 4 ) there are three reaction pathways possible, Eqns 5-7.
  • the approximate yields for the fluorine compound products discussed below are based on typical yields experienced for similar reactions in the industrial production of SFS.
  • the silicon tetrafluoride gas liberated in Eqn 5 might represent only about 15% to 25% of the fluorine from the NaF starting component, with the SFS produced in Eqn 6 might represent about 40-50% of the fluorine from the NaF starting component.
  • the silicon tetrafluoride gas can be used directly to produce silicon if sufficiently pure, or reacted further to produce SFS by first reacting with water to form FSA as:
  • Eqn 7 can be converted to SFS as in Eqn 9.
  • Eqn 7 might account for about 35% - 45% of fluorine available in the starting compound.
  • the sodium salts may be replaced by other alkali earth metal salts such as calcium for a non-limiting example.
  • silica there are many grades of silica that may be suitable for reaction according to Eqn 2B, ranging from finely divided silica "flour" to clean quartz sand used in glass production. While the present invention offers a path to produce a dual purpose solar-semiconductor Si with B and P at low levels, some silica sources almost certainly include other impurities such as titanium and iron that are known to be undesirable for photovoltaic use. Trace amounts of impurity elements with multiple valence states reduce solar cell efficiency by trapping the electrons produced by solar photons. Silica as a source for dual use silicon can be selected to have minimal traces of any undesirable impurity elements.
  • the unground silica sand grade supplied by U.S. Silica Corp. as #1 DRY has particles with more than 80 percent in the size range from 0.2 to 0.3 mm.
  • Chemical analysis indicates 99.7 weight percent SiO 2 with Fe 2 O 3 at 0.024 weight percent (wt%), Al 2 O 3 at 0.07 wt% and TiO 2 at 0.01 wt%.
  • Other elements reported as oxides at or below 0.01wt% include calcium, magnesium, sodium and potassium.
  • Any impurity elements carried over into the granular silicon produced by reaction of SiF 4 with Na (Eqn 4) will have an opportunity for additional removal during the growth of large ingots by the refining provided typically by the Czochralski (Cz) ingot growth method.
  • silica serves as the feedstock for "pure" silicon made by purification of metallurgical grade silicon (abbreviated as mgSi).
  • Metallurgical grade silicon is made by carbothermic reduction of a mixture of carbon and silica in a high temperature furnace.
  • mgSi has a relatively low purity, typically 97 weight percent Si. Refining treatment is required to improve the purity of mgSi.
  • High temperature mgSi production and purification require a substantial energy input.
  • the present invention involves low temperature aqueous reactions at or near room temperature in tanks constructed of relatively low cost materials.
  • FSA generation takes place in an aqueous mixture of acid, silica and fluoride. Likewise, precipitation of SFS by adding sodium ion to FSA takes place in an aqueous medium. Low temperature processing minimizes the opportunity for impurity transfer to the product which can occur in high temperature operations. It is also noted that the Na-SiF 4 reaction (Eqn 4) is exothermic and provides its own heat as reaction proceeds. The present invention contributes to energy savings as well as the opportunity to obtain high purity starting materials FSA and SFS for the production of pure silicon. [0065] Cost Comparison: FSA from Silica vs. Commercial FSA
  • Table 2 shows the cost benefit for using silica as silicon source by comparing the amount of silicon available from various sources and the associated cost per kilogram of available silicon. Other reagent costs are also included to obtain an overall estimate for the pure silica approach of the present invention.
  • Sources of silicon that consist essentially of silica include, without limitation, glass sand, filler sand, industrial sand, diatomaceous earth, recycled ground glass and the like. From Table 2, it is clear that silica is literally dirt cheap as a source of silicon on the basis of the cost of silica sufficient to yield 1 kg of silicon. As mentioned, the present invention does not need apatite as a source of fluoride ion for the reactions described in Eqns 2 A and 2B. The chemistry of Eqn 2A is simplified by substituting a selected source of fluoride ion in the form of a readily soluble compound with no phosphorous content.
  • fluorspar (CaF 2 ) is designated as the source of fluoride ions.
  • Acid grade fluorspar is 97 % CaF 2 and costs $220 per ton (2006 price).
  • the amount Of CaF 2 needed is 232.4 kg- mol for 28 kg-mol of silicon or 144 kg-mol of 100% FSA. Since 4.9 kg of H2SO4 are needed for each kg of SiO 2 according to Equation 2B, the cost of sulfuric acid is $ 0.635 per kilogram of Si and the cost of fluorspar is $ 2.022 per kilogram of Si.
  • Fluorspar is considered as the fluorine source only as an example.
  • the sodium fluoride by-product from the Na-SiF4 reaction (Eqn 4) is recycled to serve as the fluorine source in the Eqn 2B silica digestion reaction.
  • This embodiment provides the potential for a substantially closed loop manufacturing process where the re-cycling of such by-products reduces costs and the need for shipment of the by-product to other users.
  • HF produced in Eqn 1 can be re-cycled and used in Eqn 2B. The full assessment of integrated plant material flow will consider total mass balance and the cost of makeup NaF, if required.

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  • Chemical & Material Sciences (AREA)
  • Organic Chemistry (AREA)
  • Inorganic Chemistry (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • General Life Sciences & Earth Sciences (AREA)
  • Geology (AREA)
  • Silicon Compounds (AREA)

Abstract

L'invention concerne un procédé amélioré de production de silicium de grande pureté par la mise en réaction de sodium avec un gaz de tétrafluorure de silicium pur, afin de produire un fluorure de sodium comme sous-produit. Le gaz de tétrafluorure de silicium est formé par la décomposition d'un fluorosilicate de sodium. Le fluorosilicate de sodium est produit par précipitation quand de l'acide fluorosilicique (FSA) est mis à réagir avec le sous-produit de fluorure de sodium dans un procédé en boucle fermée. De manière analogue, on forme de préférence de l'acide fluorosilicique de grande pureté à l'aide d'une matière première constituée essentiellement de silice, par la mise en réaction du sous-produit de fluorure de sodium avec un acide afin de produire des ions fluorure réactifs.
PCT/US2009/040949 2008-04-17 2009-04-17 Procédé de production de silicium Ceased WO2009129458A2 (fr)

Applications Claiming Priority (2)

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US4590608P 2008-04-17 2008-04-17
US61/045,906 2008-04-17

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WO2009129458A3 WO2009129458A3 (fr) 2010-01-28

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CN108996507A (zh) * 2018-08-10 2018-12-14 瓮福（集团）有限责任公司 一种纳米氟硅酸钠的制备方法

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US8124039B2 (en) * 2009-01-26 2012-02-28 Vithal Revankar Process of silicon tetrafluoride gas synthesis
CN102267697B (zh) * 2010-06-04 2013-01-02 刘新林 一种钠循环法生产太阳能级多晶硅的工艺方法
US8609057B2 (en) * 2010-06-07 2013-12-17 Sri International Method for separation of components from a reaction mixture via a concentrated acid
KR101215490B1 (ko) * 2010-06-11 2012-12-26 주식회사 케이씨씨 다양한 플루오라이드 원료들과 비정질 실리카 및 황산을 이용한 사불화규소의 연속 제조방법
KR101171799B1 (ko) * 2010-06-29 2012-08-13 고려대학교 산학협력단 실리카 에칭 폐기물을 재활용하는 방법 및 메조다공성 물질을 제조하는 방법
CN117486216B (zh) * 2023-10-12 2026-03-13 多氟多新材料股份有限公司 一种氟硅酸盐的热解方法

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